While I don't use Dropbox to sync MarsEdit drafts, reading the explanation just now seems backwards to me. On every other application whose files I sync via Dropbox (and that's several), I move the application's folder (or files) to be synced to my Dropbox folder from wherever the application put it, and replace the original with a symlink to the Dropbox folder or file. To do that, you quit Dropbox on create a symlink in the dropbox and move it to both machines. To create the Symbolic Link, I use Nick Zitzmann's SymbolicLinker, which is a contextual menu service. Select the file or folder, right click on it, choose (under more...) "Make Symbolic Link".

I'm with NovaScotian: the solution is much easier than JustinBlanton suggests. The key is to have the "master" copy on Dropbox, and link to that from each machine's ~/Library/MarsEdit directory; that way, each symlink is local to its machine. (Perhaps I've got the meaning of "to" and "from" reversed, but the instructions below are correct!)

It's easiest if you are willing to throw away all of the drafts on one of the machines. If not, see below.

So, first, quit MarsEdit on all of your machines that you want to sync. Start working on the machine with the drafts that you want to save.

Now, decide on where you want to store the local drafts on your dropbox. I use ~/Dropbox/Library/MarsEdit_LocalDrafts

Next, make sure that the *enclosing* directory for this file exists. In terminal, do:

The second line puts the directory into the right place on your dropbox, and the third creates the symbolic link.

Now, on the *other* machine, as before:

> cd Library/Application\ Support/MarsEdit

If you want to save drafts from this machine, try

> mv -i LocalDrafts/* ~/Dropbox/Library/MarsEdit_LocalDrafts/

This moves the individual draft files into the Dropbox LocalDrafts folder. You may find that there are some duplicate names. Depending on which you want to keep, you can say 'y' or 'n' to the resulting prompt -- or go back and rename the file before attempting to move it, if you want to keep both.

Although I'm not actually a great fan of MobileMe, this is one of the few things for which it is useful, apart from syncing Contacts, which it is the only way of doing properly. If you activate Preferences in your MobileMe settings in System Preferences, all the pref files for your applications will be synced across connected computers. I sync my Coda and MarsEdit settings in this way, although I do use Dropbox for other settings where syncing of an actual data file is involved as opposed to settings, such as 1Password, iTunes and Aperture files.

MobileMe is a rip-off at $99, but activation keys can be had for about half that price on eBay.